Recently, contactless or noncontact IC cards or smartcards and RF ID tags are becoming pervasive. A contactless IC card is applicable to the Japanese Resident Register ID card in compliance with the ISO 14443 standard, the electronic ticketing card, employee card and electronic money which are in compliance with the FeliCa™ standard, and the like. The RF ID tag is applicable to a merchandise management system, an inventory management system and a physical distribution system which are in compliance with the ISO 15693 standard, and other systems. Moreover, it is expected that RF ID tags are provided at various locations which can be used for location services. For example, the RF ID tags may be attached to exhibits in a museum or an art gallery. In this case, when a user carrying a mobile terminal comes in front of an exhibit, the mobile terminal may detect an RF ID tag and obtain information related to the exhibit. Currently, contactless reader/writer devices are used to read from and write to the respective contactless IC cards and RF ID tags.
Passive-type information storage devices or media, such as so-called passive contactless IC cards and RF ID tags, do not include batteries, and hence need to receive power from a contactless reader/writer device through electromagnetic induction. Thus the reader/writer device is required to drive a relatively large current. Consequently, when the reader/writer device is used, for example, as a sensor at an entrance gate or for login to a notebook personal computer or a mobile terminal, it must be permanently activated, because it is not known what kind of contactless IC card or RF ID tag is brought in its proximity and when it is brought in its proximity. This causes the reader/writer device to dissipate a large amount of power, and considerably shortens the battery run time.
Yamaoka in the Japanese Patent Application Publication JP 2000-194803 (A) published on Jul. 14, 2000 discloses a reader/writer for a non-contact IC card. A proximity sensor unit for detecting an object is provided in this reader/writer. When the proximity sensor unit does not detect an object of a non-contact IC card, transmission data of a command from a control unit is not transmitted through an I/O conversion unit, an oscillation unit, a modulation unit, a power amplification part and a transmission/reception coil. Only when the proximity sensor unit detects an object of a non-contact IC card, the reader/writer performs transmission and reception.
Kobayashi and Fujii in the Japanese Patent Application Publication JP 2001-101351 (A) published on Apr. 13, 2001 disclose a reader device. When a card detection unit of the reader device detects an IC card, the reader device sends a signal to a power supply control unit to power on a control unit and an RF transmission/reception unit, to thereby transit from a low power consumption mode to a normal mode. When it cannot communicate with the card for a given time, a host controller and a reader/writer transit back into the low power consumption mode.
The PCT international publication, WO 00/65551, published on Nov. 2, 2000, discloses supplying power for reading an RF ID only when action is detected by an infrared sensor.
Sasuga et al. in the Japanese Patent Application Publication JP HEI 11-126240 (A) published on May 11, 1999 discloses a reader/writer controller which, while in a standby state, transmits command data by intermittently turning on the power for a transmission section.